论文标题
在垂直加热管中抑制湍流和行进波
Suppression of turbulence and travelling waves in a vertical heated pipe
论文作者
论文摘要
浮力可以抑制流体流动流动的湍流。由于湍流的抑制导致严重的传热恶化，这在加热和冷却应用中都是重要且不希望的现象。通常考虑垂直流动，因为轴向浮力可以帮助驱动流动。通过浮力参数$ c $测量的加热，我们的DNS表明，剪切驱动的湍流可以完全层状化或过渡到相对静止的对流驱动状态。浮力导致基本流量剖面的变平，在等热管流中，最近已将完全抑制湍流链接（Kühnen等人Nat。Phys。，2018），而扁平的层层基底轮廓增强了非线性稳定性（Marensi等人，Marensi等人，JFM，2019）。与这些发现一致，此处分析的非线性下支流式波浪溶液据信介导等温管流中的湍流，被证明被浮力抑制。层流基层流的线性不稳定性负责在考虑的雷诺数范围内以$ c \ gtrsim 4 $的相对静止对流驱动状态的出现。然而，在抑制湍流时，即在从湍流的过渡中，我们发现与He等人的分析更明显。 （JFM，2016）比上述动态系统方法更好地描述了向湍流的过渡。 He等人的层流标准。提出的，基于通过其驱动压力梯度测量的显而易见的流量的雷诺数，可以捕获关键的$ c = c_ {cr}（re）$，在该流量上将被层压化或切换到对流驱动的类型。我们的分析表明，这是削弱的卷，而不是条纹，似乎对层流至关重要。
Turbulence in the flow of fluid through a pipe can be suppressed by buoyancy forces. As the suppression of turbulence leads to severe heat transfer deterioration, this is an important and undesirable phenomenon in both heating and cooling applications. Vertical flow is often considered, as the axial buoyancy force can help drive the flow. With heating measured by the buoyancy parameter $C$, our DNS show that shear-driven turbulence may either be completely laminarised or transitions to a relatively quiescent convection-driven state. Buoyancy forces cause a flattening of the base flow profile, which in isothermal pipe flow has recently been linked to complete suppression of turbulence (Kühnen et al. Nat. Phys., 2018), and the flattened laminar base profile has enhanced nonlinear stability (Marensi et al. JFM, 2019). In agreement with these findings, the nonlinear lower-branch travelling-wave solution analysed here, which is believed to mediate transition to turbulence in isothermal pipe flow, is shown to be suppressed by buoyancy. A linear instability of the laminar base flow is responsible for the appearance of the relatively quiescent convection driven state for $C\gtrsim 4$ across the range of Reynolds numbers considered. In the suppression of turbulence, however, i.e. in the transition from turbulence, we find clearer association with the analysis of He et al. (JFM, 2016) than with the above dynamical systems approach, which describes better the transition to turbulence. The laminarisation criterion He et al. propose, based on an apparent Reynolds number of the flow as measured by its driving pressure gradient, is found to capture the critical $C=C_{cr}(Re)$ above which the flow will be laminarised or switch to the convection-driven type. Our analysis suggests that it is the weakened rolls, rather than the streaks, which appear to be critical for laminarisation.
